Magnet-core.



J. C. WOODRUFF.

MAGNET CORE.

APPLICATION FILED MAY 26. 1916. RENEWED JUNE 28.1918.

1,292,206. Patented Jan. 21,1919.

//7 Van fan- Jahn 6. WOOd/M/f York, in the county of New come 0. woonnurr, or NEW YORK, N. Y.,

mconronernn, on NEW YORK,

ASSIGNOR T WESTERN ELECTRIC N. Y., A CORPORATION -OF NEW YORK.

MAGNET-CORE.

Specification of Letters Patent.

Patented Jan. 21, 1919.

Application filed May as, 1916, Serial Nit "100,056. Renewed .Tune' as, 1918; Serial no. 242,503.

To all whom it may concern:

Be it known that I, J OHN C. Wooonurr, a citizen of the United States, residing at New York and State of New York, have invented certain new and useful Improvements in Magnet-Cores, of which the following is a full, clear, concise, and exact description.

This invention relates to magnet cores generally, and particularly to cores for loadin coils for telephone circuits. Its general ob ect is to rovide a new and improved core material which is cheap to manufacture, which is easily formed to the desired shapes, and which possesses to a high degree those characteristics most advantageous in cores for loading coils and other electrical apparatus.

The present invention may be considered an improvement upon the magnet cores and processes of manufacture described and claimed in applications for Letters Patent in the-name of James Buckner Speed, Serial No. 89,409, filed April 6, 1916, for improvements in magnet cores, and in the name of Gustaf W. Elmen, SeriaL No. 89,467, filed April, 6, 1916, for improvements in magnet cores, both of which applications are assigned to the same assignee as the present application.

The present invention is the result of the discovery that the specific resistance of a core made of particles of finely divided magnetic material insulated from one another and formed into a solid mass by great pressure, is considerably increased if, before be ing coated with insulating material, said particles are coated with some other metal such as lead aluminum or zinc. The present invention, therefore, relates to a magnet core and method of making the same, characterized by the fact that articles of magnetic material are first given a coating of some other metal, are then coated with insulating material, and are finally compressed to form a core or core material from which cores can be made.

In the drawing, Figure 1 is a perspectlve view of a section of loading coil core made in accordance with the present invention, and Fig. 2 shows a plurality of these sections assembled to form a complete core. It will be understood, however, that this is merely illustratlve, and that the invention is not limited to the production of this form of core, but is adapted for the making of cores of many forms.-

In the making of loading coil cores, the present invention is preferably carried out in the following manner: Magnetic material. such as electrolytic iron, obtained in any well-known manner (for example from a cell containing a bath of ferrous ammonium sulfate), after being broken into small pieces. is reduced to small particles by grinding in a ball mlll. Experience has shown that, for the best results, the particles used in coremaking should not be larger in size than what W111 pass through what is known as 80- mesh screen, and about: forty per cent. (40%) of them should be so small as to be capable of passing through a 200-mesh screen.

Electrolytic iron particles of this size are heated in any suitable form of furnace to anneal them and to drive oif any occluded gases, principally hydrogen. Oxidation of the iron particles during annealing may be prevented in any suitable manner, for example, by packing the iron particles in an iron box which is sealed by inverting over it another iron box and filling the space between the sides of the boxes with iron oxid. The annealing temperature preferably employed is 1400 Fahrenheit. If the box is not opened until it has cooled to room or atmospheric temperature practically no oxidation of the iron particles takes place during annealing. In case the mass of particles ca es during the annealing, it may be again reduced in any suitable manner to particles small enough to pass through an SO-mesh screen.

The annealed iron particles are then mixed with pieces of zinc, and the mixture is tumbled in a drum for a considerable length of time, say for thirty-six (36) hours. A satisfactory form of zinc for this purpose is so-called feathered-zinc, which is obtained by pouring molten zinc into water. Upon being removed from this drum, the larger zinc pieces are separated from the comm,

solution is one obtained by disso alcohol, and heating 'iron particles by sifting iron particles.

the mixture first through a coarse screen, such as one of 16- mesh, and then through a screen of SO-mesh which removes substantially all of the zinc particles and allows the iron particles to pass through.

' To the mass of annealed zinc-coated iron particles obtained in the manner just described, is added a thin solution of insulatperature of 160 one hour.

alcohol I fromiron particles and shellac solution, any satisfactory method may be employed, for example, the mass may be slowly tumbled in a tumbling barrel through which a current of air isdrawn. After the alcohol has been evaporated in this manner, the annealed Preferably, pressures as high making loading coil 'zinc-coated shellac-coated particles are then,

ready for compression either into bulk material from which cores maybe made, or directly into the desired form of core.

The remainder of the method of making magnetcores is substantially the same as that described in the Speed application, Serial No. 89,409, above referred to; but

in order that this application'may contain a full disclosure of the best method of carrying out the present invention, the remainin steps of the method will be herein describe The mold and press employed in the compressing process should be/apable ofstanding and exerting exceedingly high pressures.

as two hundred thousand pounds to the square inch should be employed; and for the best results as to uniform density, the thickness of any core section, in the direction in which.

the pressure is exerted in forming it, should usually not exceed approximately one-quarter of an inch.

In practice, it has been found desirable in cores, to use core sections having a thickness of about 0.2 inches and to use about acore; a suitable insulating material such as paper, lacquer, or shellac being interposed between the sections. Fig. 1 shows such a core section or ring, and, Fig. 2

. coil core of 'sistance, an extremely low hysteresis char- I coating of insulating five sections in building up shows the built-up core. As shown, the outside ed es of the outside core sections are rounded, axis being desirable in order that the windings may closely conform to the surface of the core.

It has been found that cores made in the -manner above described are strong mechanicall and stable chemically; specific gravitiy nearly-that o proximately and that their is approximately 7 which is undivided iron, which is ap- 7 .7. Electrically, a loading this'kind has high specific reacteristic'," excellent magnetic stability, and comparatively high permeability, as understood in telephone loading coil design.

Experiments have shown that cores made in the manner described have a higher specific resistance than ners described in Speed application Serial No. 89,409, and Elinen application, Serial No. 89,467, hereinbefore referred to.

What is claimed is:

1. A magnet core composed of finely divided iron particles, a coating of some other metal on said particles, and insulating material separating'the coated iron articles.

2. A magnet core composed of finely divided iron particles, a coating of some other metal on said particles, and insulating ma'- terial separatin said compound approximately 7. 4 *3. A magnet core composed of finely divided iron particles, a coating of zinc on said particles, and insulating material separating said zinc-coated iron particles.

4. A magnet vided iron particles, a coating of zinc on said particles, and a coatin of shellac on said zincecoated particles, said compound having a specific gravity of approximately 7.

5. The method of making magnet cores, which consists in covering iron particles with a coating of some other metal, then covering said coated iron particles with a material, and then formin a mass of said coated particles into a solid ody by pressure suflicient to give it a specific gravity of approximately 7 6. The method of making magnet cores, which consists in covering particles of magnetic material with a coating of zinc, then covering said zinc-coated particles with a coating of insulating material, and then forming amass of said particles into a solid body by pressure sufiicient to 've it a spe-' cific gravity of approximately? 7 The method of making magnet cores, which consists in coverin particles of iron the coated iron particles, aving a specific gravity of with a coating of zinc, t en coverin said zinc-coated particles with a coating 0 shellac, and then forming a mass of said parcores made in the mancore composed of finely diticles into a solid body by pressure sufficient to give it a specific gravity of approximately 7. v

8. The method of making magnet cores, which consists in covering particles of iron with a coating of zinc, wetting said zinccoated particles with a solution of shellac and alcohol, evaporating the alcohol from the mixture, and submitting a mass of said coated particles to ressure sufiicient to give 10 the mass a spec' c gravity of approximately 7. i In witness whereof, I hereunto subscribe my name this 24th day of May A. D., 1916.

JOHN o. WOODRUFF. 

